Chapter 4

Dilute and Leaden, the p-Locus, Ruby-Eye, and Ruby-eye-2

IV. Ruby-Eyed-2 (ru-2)

A. Origin and Description

In 1966 Lilly reported a recessive coat-color mutation which, because it was phenotypically identical to ruby-eye, he designated
ru-2. The deviant occurred in a substrain of C57BL/6 and was shown to be located near pink-eyed on chromosome 7. Eicher (
1970a), in a more detailed linkage analysis, reported
ru-2 to reside 3 cM from
p and 17 cM from
c with the order being
c
p
ru-2. Like
ru,
ru-2 produces a grayish-brown color in the eumelanin region of the agouti hair and dark red eyes.
22 Phaeomelanin is only slightly affected. The influence of
ru-2 at the cellular level has unfortunately not been investigated (
Eicher, 1970a).

B. Other Alleles (Maroon and Haze)

Recently it has been discovered that maroon (
mr) and haze (
mrhz), two recessive coat-color determinants which were believed to be inherited independently from
ru-2, are actually allelic with
ru-2 (
Eicher and Fox, 1977). Hence these two mutants are now designated
ru-2mr (maroon) and
ru-2hz (haze).

Maroon arose spontaneously in a "lactation" stock (
N. Bateman, 1957). The eyes of
ru-2mr/ru-2mr mice are colorless at birth, but darken to a rich maroon. The coat color of maroon mice varies from almost
normal to extreme pallid, even among sibs, and darkens with age. The underfur and isolated hairs of this mutant are often silvered (
N. Bateman, 1957). According to Roderick (
1973,
1975), nonagouti maroon (
a/a;ru-2mr/ru-2mr) animals look very much like nonagouti buff (
a/a;bf/bf) mice (see
Chapter 6, Section IV, B). Nevertheless, these mutants can be readily distinguished from each other by the fact that whereas
a/a;ru-2mr/ru-2mr mice have light ears, a solid belly, and translucent eyes,
a/a; bf/bf animals have
darker ears, a belly lighter than the rest of the coat, and opaque eyes (
Davisson, 1977). According to Davisson "the eyes must be observed by examining the mouse in profile against light." the double homozygote
a/a;ru-2mr/ru-2mr;bf/bf has a distinctly lighter coat color than either homozygote alone (
Roderick, 1975;
Davisson, 1977). Maroon has been reported to interact with silver (
si) in the F1 (
N. Bateman, 1957) (see also
Chapter 6, note 11).

Haze was originally described by Dickie (
1965b) after it arose spontaneously in the DBA/2J strain. This mutation is characterized at birth by light colored eyes. In the adult the
hair color is brownish and the ventrum is white. In 1974 E.S. Russell demonstrated that haze was allelic to maroon.